1. Field of the Invention
The present invention relates to a wireless power feeding system including a power-receiving device.
2. Description of the Related Art
A method called a magnetic resonance method attracts attention as a method for feeding power to an object (hereinafter also called a power-receiving device) not in contact with a power supply (hereinafter also called a power-transmitting device) (such a method is also called a contactless power feeding method, a wireless power feeding method, or the like). The magnetic resonance method is a method in which resonance coils provided in a power-transmitting device and a power-receiving device are put in magnetic resonance with each other to form an energy propagation path. The magnetic resonance method yields a longer power transmittable distance than other methods (e.g., an electromagnetic induction method and a field induction method). For example, Non-Patent Document 1 discloses that in the magnetic resonance method, transmission efficiency is about 90% when the distance between the resonance coils is 1 m, and is about 45% when the distance between the resonance coils is 2 m.